Instrument for high throughput measurement of material physical properties and method of using same

(12)

United States Patent

Hajduk

et

aI.

(54) INSTRUMENT FOR HIGH THROUGHPUT MEASUREMENT OF MATERIAL PHYSICAL PROPERTIES AND METHOD OF USING SAME

(75) Inventors: Damian Hajduk, San Jose, CA (US); Eric Carlson, Palo Alto, CA (US);

J.

Christopher Freitag, Santa Clara, CA (US); Oleg Kolosov, Cupertino, CA (US); James R. Engstrom, Ithaca, NY (US); Adam Safir, Berkeley, CA (US); Ravi Srinivasan, Mountain View, CA (US); Leonid Matsiev, San Jose, CA (US)

(73) Assignee: Symyx Technologies, Inc., Santa Clara, CA(US)

( *) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.c. 154(b) by 440 days.

(21) Appl. No.: 09/779,149 (22) Filed:

(65)

Feb. 8,2001

Prior Publication Data

US 2002/0029621 Al Mar. 14,2002

Related U.S. Application Data

(62) Division of application No. 09/580,024, filed on May 26, 2000.

(51) Int. CI.7 ... GOiN 31/00; GOIN 3/00;

G01N 3/08 (52) U.S. CI. ... 436/2; 436/55; 435/DIG. 1; 435/DIG. 2; 435/DIG. 9; 73/760; 73/788; 73/789; 73/826; 73/841; 73/847 (58) Field of Search ... 435/7.1, DIG. 1,

(56)

435/2, DIG. 9; 436/2, 55; 73/760, 788, 789, 826, 841, 847 References Cited

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(10)

Patent No.:

(45)

Date of Patent:

US 6,936,471 B2

Aug. 30, 2005

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(Continued)

FOREIGN PATENT DOCUMENTS

0317356A2 5/1989 02297040 A 12/1990

(Continued) OTHER PUBLICATIONS Translation of JP-3-122544 (stapled with Patent).* Translation of JP-4-366744 (stapled with Patent).

*

(Continued)

Primary Examiner-Padmashri Ponnaluri

Assistant Examiner-My-Chau T Tran

(74) Attorney, Agent, or Firm-Dobrusin & Thennisch, PC

(57) ABSTRACT

An apparatus and method for screening combinatoriallibrar-ies of materials by measuring the response of individual library members to mechanical perturbations is described. The apparatus generally includes a sample holder for con-taining the library members, an array of probes for mechani-cally perturbing individual library members, and an array of sensors for measuring the response of each of the library members to the mechanical perturbations. Library members undergoing screening make up a sample array, and indi-vidual library members constitute elements of the sample array that are confined to specific locations on the sample holder. During screening, the apparatus mechanically per-turbs individual library members by displacing the sample array (sample holder) and the array of probes. Typically, all of the elements of the sample array are perturbed simultaneously, but the apparatus also can also perturb individual or groups of sample array elements sequentially. The flexible apparatus and method can screen libraries of materials based on many different bulk physical properties, including Young's modulus (flexure, uniaxial extension, biaxial compression, and shear); hardness (indentation), failure (stress and strain at failure, toughness), adhesion (tack, loop tack), and flow (viscosity, melt flow indexing, and rheology), among others.

US 6,936,471 B2

Page 2

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lP JP lP WO WO WO WO WO WO WO WO WO WO

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*

5/1991 5/1991

* 12/1992 4/1996 4/1998 4/1999 3/2000 4/2000 6/2000 7/2000 9/2000 11/2000 10/2001

... G01N/3/oo

... GOlN/3/00

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Materials, vol. 26, No.7, pp. 852-858, 1997.

"Ultramacroindentation Apparatus for the Mechanical Char-acterization of Thin Films" P.E. Wierenga and A..T..T. Fran-ken, 1. Appl. Phys., 55 (12), pp. 4244-4247, Jun. 15, 1984. "Micro hardness Studies of Polymers and Their Transitions,"

F.J. Balta Calleja, TRIP, vol. 2, No. 12, pp. 419-425, Dec.

1994.

"Evaluation of Young's Modulus of Polymers from Knoop Microindentation Tests," E. Amitay-Sadovsky and H.D. Wagner, Polymel; vol. 39, No. 11, pp. 2387-2390, 1998. "Standard Test Method for Rubber Property-International Hardness," ASTM, D 1415-88, Feb. 1989.

"DMA 2980 Dynamic Mechanical Analyzer," http://www. tainst.com/dma2.html, Dec. 29,2000.

"Introducing the New DMTA V!," http://www.rheometric-scientific.com/dmta V.htm, Dec. 29, 2000.

Robert H. Lacombe and Jeremy Greenblatt, "Mechanical Properties of Thin Polyimide Films," Proc. Tech. Conf. Polyimides (First) 1982, published in Polyimides: Synth.,

Charact., Appl., pp. 647-668, 1984.

U.S. Appl. No. 09/939,404 entitled "High Throughput Mechanical Property and Bulge Testing of Material Librar-ies," (D. Hajduk et al.) filed Aug. 24, 2001.

U.S. Appl. No. 09/939,252 entitled "High Throughput Mechanical Rapid Serial Property Testing of Material Libraries," (P. Mansky) filed Aug. 24, 2001.

U.S. Appl. No. 09/939,139 entitled "High Throughput Fab-ric Handle Screening," (M. Kossuth et al.) filed Aug. 24, 2001.

U.S. Appl. No. 09/939,149 entitled "High Throughput Rheo-logical Testing Of Materials" (Paul Manksy et al.) filed Aug. 24,2001.

US 6,936,471 B2

Page 3

The family of applications for U.S. App1. No. 09/174,856 titled "Graphic Design of Combinatorial Material Libraries" (Lacy, et a1.) filed Oct. 19, 1998.

U.S. App1. No. 09/578,997 entitled "High Throughput Vis-cometer and Method of Using Same" filed May 25, 2000. Odian, Principles of Polymerization, 3rd Ed., John Wiley &

Sons, Inc. (1991).

Timoshenko, S., Theory of Plates and Shells, McGraw-Hill, New York 1940.

European Search Report dated Dec. 10, 200l.

U.S. App1. No. 09/420,334 entitled "Graphic Design of Combinatorial Material Libraries" (Lacy, et a1.) filed Oct. 18, 1999.

U.S. App1. No. 09/305,830 titled "Synthesizing Combina-torial Libraries of Materials" (Rust, et a1.) filed May 5,1999. U.S. Appl. No. 09/550,549 entitled "Automated Process Control And Data Mangement System And Methods" (Cre-vier, et a1.) filed Apr. 14,2000.

U.S. App1. No. 09/755,623 entitled "Laboratory Database System and Methods For Combinatorial Materials Research" (Dorsett, Jr., et a1.) filed Jan. 5, 200l.

The family of applications for U.S. App1. No. 09/227,558 entitled, "Apparatus and Method of Research for Creating and Testing Novel Catalysts, Reactions and Polymers" (Turner et a1.) filed Jan. 8, 1999.

U.S. App1. No. 09/235,368 entitled "Polymerization Method From the Combinatorial Synthesis and Analysis of Organo-metallic Compounds and Catalysts" (Weinberg et a1.) filed Jan. 21, 1999.

Provisional U.S. Appl. No. 60/122,704 entitled "Controlled, Stable Free Radical Emulsion and Water-Based Polymer-izations" (Klaerner et a1.) filed Mar. 9, 1999.

The family of applications for U.S. App1. No. 09/156,827 entitled "Formation of Combinatorial Arrays of Materials Using Solution-Based Methodologies" (Giaquinta et al.) filed Sep. 18, 1998.

The family of applications for U.S. Appl. No. 09/567,598 entitled "Polymer Libraries on a Substrate, Method for Forming Polymer Libraries on a Substrate and Character-ization Methods with Same" (Boussie et al.) filed May 10, 2000.

U.S. Appl. No. 09/579,338 entitled "Rheo-Optical Indexer and Method of Screening and Characterizing Arrays of Materials" (Carlson et al.) filed May 25, 2000.

Bowlt, C., "A Simple Capillary Viscometer" Physics Edu-cation, Mar. 1975, vol. 10, No.2, pp. 102-103.

Young,

w.e.,

Roark's Formulas for Stress and Stain, 1989. Ali, S.1. and Shahida Begum, "Fabric Softeners and Softness Perception", Ergonomics, v.37, No.5, pp. 801-806 (1994). Osterberg, Peter M. and Stephen D. Senturia, "M-TEST: A Test Chip for MEMS Material Property Measurement Using Electrostatically Actuated Test Structures," Journal of Microelectromechanical Systmes, vol. 6, No.2, Jun. 1997. Kim 1.0. and B. Lewis Slaten, "Objective Assessment of Fabric Handle in Fabrics Treated With Flame Retardants," Journal of Testing and Evaluation, JTEVA, vol. 24, No.4, Jul. 1996, pp. 223-228.

Raeel, Mastura and Jiang Liu, "An Empirical Model for Fabric Hand" Textile Research Journal 62, 1, pp. 31-38 (1991).

Pan, Ning and

K.e.

Yen, "Physical Interpretations of Curves Obtained Through the Fabric Extraction Process for Handle Measurement," Textile Research Journal 62(5), pp. 279-290 (1992).

"Handle-O-Meter", Thwing-Albert Instrument Company, Philadelphia, PA.

Grover, G. et aI., "A Screening Technique for Fabric Handle",1. Text. Inst., 1993,84 No. 1. Textile Institute, pp. 486-494.

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1

INSTRUMENT FOR HIGH THROUGHPUT MEASUREMENT OF MATERIAL PHYSICAL

PROPERTIES AND METHOD OF USING SAME

This application is a divisional of copending U.S. patent application Ser. No. 09/580,024, filed May 26, 2000, which is herein incorporated by reference for all purposes.

BACKGROUND 1. Technical Field

The present invention relates to an apparatus and method for determining physical characteristics of an array of mate-rials as functions of mechanical perturbations and environ-mental conditions.

2. Discussion

Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compounds-commonly known as libraries-and to tech-niques and instruments for evaluating or screening libraries for desirable properties. Combinatorial chemistry has revo-lutionized the process of drug discovery, and has enabled researchers to rapidly discover and optimize many other useful materials.

Scientists realized that efficient screening techniques were essential for any successful combinatorial research effort. However, since much of the original work in combinatorial chemistry focused on biologically active compounds, early researchers typically employed conventional biological assays as screening methods. Many of these assays were ideally suited for screening combinatorial libraries because they required little or no sample preparation and they could generate useful results using small sample sizes (a mg or less) generally produced in a combinatorial synthesis.

But as researchers began applying combinatorial methods to develop novel non-biological materials, they increasingly found that conventional instruments and methods for char-acterizing materials were often unsatisfactory for screening. For example, instruments for characterizing physical prop-erties of materials-viscometers, rheometers, dynamic analyzers, and other mechanical property test instruments-are generally unsuitable for screening purposes because they were designed to process one sample at a time. Although the throughput of these serial instruments would likely benefit from automation, many mechanical property test instru-ments require time-consuming sample preparation, demand more sample than is ordinarily prepared in a high speed research program, and exhibit sluggish environmental control, making such instruments impractical for use as screening tools. Furthermore, the long time scales associated with measuring mechanical properties of polymers, ceram-ics and other engineered materials often make serial approaches unsuitable as screening methods.

Moreover, competitive pressures are forcing scientists to continually expand their set of screening tools. Many mate-rial scientists have embraced combinatomate-rial methodologies because the techniques allow them to develop novel mate-rials in a fraction of the time as conventional discovery methods. This has allowed researchers to tackle a wider range of material design challenges and to consider a broader set of characteristics that ultimately translates into improved material performance. Of course, new design challenges and additional screening criteria mean that labo-ratories must acquire more screening tools, which if pur-chased as separate instruments, might offset cost savings associated with combinatorial methods.

10

15

2

Thus, there exists a need for versatile instruments and techniques for screening combinatorial libraries, and espe-cially instruments and methods for measuring physical prop-erties of materials. The present invention, at least in part, satisfies that need.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for screening combinatorial libraries that addresses many of the problems encountered when using conventional instru-ments. For example, the disclosed apparatus can measure physical properties of library members in parallel and can perform tests on small amounts of material, which are easily prepared by automated liquid and/or solid handling tech-niques. Compared to conventional instruments, the dis-closed apparatus affords faster sample loading and unloading, for example, through the use of disposable sample arrays and test probes. The present invention is operationally flexible, and permits a single instrument to

20 perform many different material tests through proper selec-tion of sample array format and test probe design. Rapid serial measurements may also be performed.

Thus, one aspect of the present invention provides and

25 apparatus for measuring bulk physical properties of an array of material samples. The apparatus includes a moveable sample holder for containing the array of material samples, and an array of probes for mechanically perturbing the array of material samples. The apparatus also includes an actuator

30 for translating the moveable sample holder and the array of material samples. The actuator moves the array of material samples in a direction normal to a plane defined by the ends of the probes so that the material samples contact the probes. In addition, the apparatus includes a sensor for monitoring

35 the response of the materials to mechanical perturbation by the probes. Typical sensors include force sensors.

A second aspect of the present invention provides a system for screening a combinatorial library of materials by measuring bulk physical properties of the materials. The

40 system includes an array of material samples and probes for mechanically perturbing the samples. Depending on the particular physical property being tested, the array includes materials deposited at predefined regions on flexible or rigid substrates, or materials contained in a group of vessels. The

45 system also includes an actuator for translating the array of material samples in a direction normal to a plane defined by the ends of the probes so the material samples contact the probes. The system also includes a sensor for monitoring the response of the array of material samples to mechanical

50 perturbations by the probes.

A third aspect of the invention provides a method of screening a combinatorial library of materials. The method includes providing an array of material comprising at least five individual samples, and mechanically perturbing the

55 array of materials by contacting at least two of the material samples with probes simultaneously. In addition, the method includes monitoring responses of the samples during the mechanical perturbations. Depending on type of mechanical perturbation, the method can screen libraries of materials

60 based on measurements of many different bulk physical properties. For example, the inventive method can measure physical properties related to Young's modulus-including flexure, uniaxial extension, biaxial compression, and shear. In addition, the method can measure physical properties

US 6,936,471 B2

3

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment of a parallel dynamic mechanical analyzer (PDMA).

FIG. 2 shows a cross-sectional view of an isolation block module that separates the probe test fixtures and the sample array from the force sensors.

4

FI G. 23 shows a partial cross-sectional view of a second embodiment of a sample holder, a material sample array, and test fixtures that the PDMA of FIG. 1 can use to screen libraries of materials based on adhesion.

FIG. 3 shows a close-up cross sectional view of the probe shown in FIG. 2, and illustrates the use of a permanent magnet to attach the test fixture to the threaded cylindrical 10

core of the composite shaft.

FIG. 24 shows a representative plot of force and sample holder displacement versus time for adhesion measurements using the sample holder, the material sample array and test fixtures shown in FIG. 22.

FIG. 25 is a graph of the results from the example. DETAILED DESCRIPTION OF THE

PREFERRED EMBODIMENTS FIG. 4 shows a cross sectional view of two adjacent

isolation block modules, and illustrates interactions of probes and force sensors.

Overview of Apparatus and Method FIG. 5 shows a perspective bottom view of one of the 15

sensor boards.

The present invention comprises a system and method for screening combinatorial libraries of materials by measuring the response of individual library members to mechanical perturbations. Throughout and in accord with this specification, the number of member of a combinatorial library of materials may vary depending on the embodiment FIG. 6 shows a top view of a portion of one of the sensor

boards.

FIG. 7 is a flow chart for the data acquisition control. FIG. 8 shows a cross-section view of representative components of material sample array and test fixtures that the PDMA of FIG. 1 can use to screen libraries of materials based on flexure measurements.

20 being practiced. Generally, an array of materials comprises

a plurality of materials for which a property measurement is desired. In some embodiments, an array of materials will comprise 8 or more, 16 or more, 24 or more or 48 or more FIG. 9 shows typical results of a flexure measurement for 25

a single element of a material sample array.

materials, each of which is different from the others. Arrays of materials and methods of making such arrays are described in detail, for example, U.S. Pat. Nos. 6,004,617 FIG. 10 shows typical results of flexure measurements

made in a "direct" mode.

FIG. 11 shows typical results of flexure measurements made in an "oscillatory" mode.

FIG. 12 shows a graph of stiffness versus displacement of the first translation actuator (coarse stage).

FIG. 13 shows a cross-section view of a portion of a material sample array and test fixtures that the PDMA can use to screen libraries of materials based on uniaxial exten-sion or biaxial compresexten-sion measurements.

FIG. 14 shows a cross-section view of representative components of material sample array and test fixtures that the PDMA of FIG. 1 can use to screen libraries of materials based on shear force measurements.

FIG. 15 shows a cross-section view of a portion of a material sample array and a representative test fixture that the PDMA of FIG. 1 can use to screen libraries of materials based on indentation measurements.

FIG. 16 shows force-displacement curves for indentation measurements of melt-pressed polystyrene samples mounted on a rigid substrate.

FIG. 17 shows a cross-sectional view of a portion of a material sample array and a representative test fixture that the PDMA of FIG. 1 can use to screen libraries of materials based on viscosity or viscosity-related measurements.

FIG. 18 shows a cross-sectional view of a portion of a material sample array and representative test fixtures that the PDMA of FIG. 1 can use to screen libraries of materials based on melt flow indexing.

FIG. 19 shows real and imaginary parts, F'(co) and F"(co), of the force exerted on test fixtures by fluid motion of a polyisobutylene sample.

FIG. 20 shows F'( OJ) for three polyisobutylene standards. FIG. 21 shows a perspective view of test fixture for an embodiment for adhesive failure.

FIG. 22 shows a cross-sectional view of a first

embodi-and 6,030,917 embodi-and U.S. patent application Ser. No. 09/227, 558, filed Jan. 8, 1999, all of which are incorporated herein by reference for all purposes. The materials in the arrays

30 may be any type of material for which a property

measure-ment is desirable. Examples of the types of materials that may be in an array include non-biological polymers (such as polyethylene, polypropylene, polystyrene, polymethacrylic acid, polyacrylamide, polymethylmethacrylate and the like,

35 including copolymers or higher order polymers of the same monomers), metals (including all types of alloys), composites, etc. The materials in the array may be in various forms, including amorphous, crystalline and mixtures thereof. The only limitation on the type of material is that the

40 material must be capable of being deposited in a manner compatible with the property testing described herein. Those of skill in the art will appreciate from this specification that members of the array may be the same or different materials. Also, standards (such as calibration standards) or blanks

45 may be employed in the array for known scientific purposes. Relative comparison of the properties of members of the array is a particularly useful embodiment of this invention. Throughout this specification, the specific embodiment discussed in detail is a ninety -six parallel embodiment. This

50 particularly preferred embodiment has many detailed

features, which may not be necessary in other embodiments of this invention. For example, force sensors are placed remotely to the samples and are set at certain spacing. Those of skill in the art can easily modify such design parameters

55 for other embodiments, such as by placing the sensors at

other spacing, not placing the sensors substantially in a plane and not placing the samples remote to the sensors (e.g., using an integrated probe and sensor). These are design choices for the present invention and describe other

embodi-60 ments of the invention.

ment of a sample holder, a material sample array, and test 65

fixtures that the PDMA of FIG. 1 can use to screen libraries

US 6,936,471 B2

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fixture. In terms of throughput, a single material (e.g., a sample) may have up to ten different properties measured simultaneously. In addition, up to 96 materials may have one or more properties measured simultaneously in 10 minutes or less, preferably 5 minutes or less and even more prefer-ably in 1 minute or less. In some embodiments, throughput of 30 seconds or less or even 10 seconds or less may be accomplished for an array of the sizes discussed herein, e.g., up to 96 materials in the array.

Generally, the samples are associated with specific loca- 10

tions or regions of the sample holder such that the location of individual samples may be known. Thus, samples may be contained by the sample holder, placed on the specific locations of the sample holder or fixed to the sample holder (e.g., if the sample holder is replaceable) or otherwise 15

specifically located. The method of knowing the location of

6

environmental chamber that encloses the sample holder, the sample array, and the probes. As discussed below, the system may locate the sensors outside of the environmental cham-ber if their performance is strongly influenced by any of the environmental control variables, such as temperature.

The system uses software running on a general-purpose computer to control the mechanical perturbations and to acquire and record the response of the sample array elements to the mechanical perturbations. Computer software also regulates conditions in the environmental chamber, if present. A" discussed below, one or more data acquisition boards, which are under the direction of the software, link the computer to the peripheral control elements, sensors, and so on.

The versatile system can screen libraries of materials based on many different bulk physical properties. For example, the system can measure physical properties related to Young's modulus-including flexure, uniaxial extension, biaxial compression, and shear. In addition, the system can measure physical properties related to hardness (indentation), failure (stress and strain at failure, toughness), adhesion (tack, loop tack), and flow (viscosity, melt flow indexing, and rheology), among others. As described below, the system can choose from among many screening criteria an individual sample is not critical to this invention and is

described herein based on the samples being contained in the sample holder for illustration purposes only. Also generally, preferred embodiments of attachment means are described 20

for various parts (such as clamping, threading, magnetic coupling, springs, etc.), but those of skill in the art will appreciate that this is simply a matter of design choice and the invention herein is not limited to the specific

embodi-ments described in detail. 25 or physical properties by selecting the proper sample array format and probe design.

As used in this disclosure, the term "mcchanical pertur-bations" generally refers to controlled straining and/or shearing of a library member. The actual displacement of the material may be small (for example, about thirty,um or less). The system generally includes a sample holder for contain-ing or securcontain-ing the library members, one or more probes for mechanically perturbing individual library members, and one or more sensors for measuring the response of each of the library members to the mechanical perturbations. Library members undergoing screening make up a sample array, and individual library members constitute elements of the sample array that are confined to specific locations on the sample holder. Although the system can screen libraries of varying size, a most preferred embodiment is a library comprising an eight-by-twelve rectangular array of material samples in which, similar to a standard ninety-six well microtiter plate, the centers of adjacent array elements are spaced nine-mm apart.

During screening, the probes mechanically interact with the elements of the sample array. In some embodiments the probes have about the same lateral spacing as the elements of the sample array so that there is a one-to-one correspon-dence between individual probes and sample array elements. In addition, since the sample array and the ends of the probes also define two generally planar surfaces, the system can perturb all of the sample array elements simultaneously by displacing the sample array (sample holder) and/or the probes in a direction normal to the two surfaces. If adapted

Parallel Dynamic Mechanical Analyzer (PDMA)

FIG. 1 shows a prospective view of a parallel dynamic mechanical analyzer (PDMA) 100 that can be used to screen

30 a library of materials by measuring responses of the

mate-rials to mechanical perturbations. The PDMA 100 includes a sample holder 102 for containing or securing the library members, probes 104 for perturbing individual library members, and sensors 106 (e.g., force sensors) for

measur-35 ing the response of each of the library members to the mechanical perturbations. The library members comprise a sample array (not shown) in which individual library mem-bers constitute elements of the sample array that are con-fined to specific locations 108 on the sample holder 102. The

40 particular sample holder 102 shown in FIG. 1 contains a sample array comprised of an eight-by-twelve rectangular array of material samples located on nine-mm centers. But in general, the PDMAcan analyze sample arrays having two or more elements, and preferably, at least eight elements to

45 ensure adequate screening throughput. The PDMA 100 generally has as many probes 104 as desired, for example there may be as many as there are samples in the array, although for clarity, FIG. 1 shows only two probes 104. In the embodiment shown in FIG. 1, each of the probes 104 has

50 about the same lateral spacing as the elements of the sample

array so that one probe 104 is associated with one sample array element. Alternatively, the PDMA may employ fewer probes 104 than sample array elements, so that a probe or group of probes perturbs multiple sample array elements. to perturb all of the elements simultaneously, the system

may include a rectilinear translation stage that is attached to the sample holder or the probes. In other embodiments, the system may perturb individual or groups of sample array elements. In these embodiments, the system may include a translation mechanism capable of three-dimensional motion, which is attached to a single probe, to a group of probes, or 60

to the sample holder.

55 Alternatively, there may be more probes than samples.

The PDMA 100 includes first 110 and second 112 trans-lation actuators for displacing the sample array in a direction normal 114 to surfaces containing the sample array and the ends of the probes 104. The first translation actuator 110, which is attached to the sample holder 102 via a housing 116 that surrounds the second translation actuator 112, provides relatively coarse displacement of the sample holder 102. A useful first translation actuator 110 includes a motorized translation stage available from POLYTEC PI under the trade name M -126 Translation Stage, which has a translation range of twenty-five mm and a resolution of 0.1 flm. The second translation actuator 112, which is attached directly to Since the bulk physical properties of materials can depend

strongly on environmental conditions-temperature, pressure, ambient gas composition (including humidity), electric and magnetic field strength, and so on-the screen- 65

US 6,936,471 B2

7

the sample holder 102, provides relatively fine displacement of the sample holder 102. A useful second translation actuator 112 includes a preloaded piezoelectric stack avail-able from Polytec PI under the trade name P-753 LISA Linear PZT Stage Actuator, which has a translation range of

30,um and can provide an 100-N pushing force and a 20-N pulling force. Other embodiments for these parts will be within the scope of those of skill in the art. The PDMA 100 typically controls the first 110 and second 112 translation actuators using a DC motor controller and an amplifier/ position servo controller, respectively, which are linked to a general-purpose computer (not shown). In an alternative embodiment, the first 110 translation actuator is mounted on an x-y translation stage (not shown), which allows move-ment of the sample holder 102 in a direction about parallel to the surfaces containing the sample array and the ends of the probes 104. This latter embodiment is useful when the sample holder 102 must be moved laterally to align different groups of sample array elements with the probes 104 during screening-i.e., when the PDMAemploys fewer probes 104 than sample array elements and the probes 104 are station-ary.

Each of the probes 104 includes a test fixture 118 that contacts one of the sensors 106 through a solid or composite shaft 120 shown in phantom in FIG. I. Each shaft 120 passes through an aperture 122 in an isolation block module 124 that separates the probe test fixture 118 from the sensor 106. For clarity, FIG. 1 shows only two isolation block modules 124, although this embodiment of the PDMA 100 ordinarily includes twelve such modules 124-one isolation block module 124 for each row of eight probes 104. Alternatively, the PDMA may include a single isolation block for sepa-rating the probe test fixtures 118 from the sensors 106. For reliable measurements, each test fixture 118 should contact its associated sample array element in a specific location 108 on the sample holder 102. This requires a mechanism for locating the composite shaft 120 along a line extending from the center 126 of a particular sensor 106, normal to the surface of the sample array. Although conventional linear bearings can be used to align the composite shaft 120, friction between the linear bearings and the shaft 120 limits the displacement resolution at low force levels. In addition, the PDMAcan also use air bearings, but the size and expense

8

strips 150. Since the diameters of the core 158 and the holes in the flexure strips 150 are about the same, the periphery of the holes are clamped between the abutting ends of the upper 160, intermediate 162, and lower sections of the sheathing. The flexure strips 150 are also clamped along the periphery of each aperture 122, adj acent interfaces between the upper 152, intermediate 154, and lower segments 156 of the isolation block module 124. The resulting clamped mem-branes or diaphragms 166, which span annular gaps 168

10 between the shafts 120 and the isolating block module 124, support and align the probes 104.

The geometry of the diaphragms 166 makes each of the flexure strips 150 compliant for displacements normal 114 to the surface supporting or containing the sample array, but

15 mechanically stiff for displacements parallel to the sample

array. The use of two flexure strips 150 also makes each combination of shaft 120 and diaphragms 166 mechanically stiff for angular displacements away from the direction normal 114 to the surface of the sample array. Moreover,

20 through proper selection of materials and dimensions, the

flexure strips 150 exhibit effective spring constants-for displacements normal 114 to the sample array-substantially less than effective constants of the sensors 106. In this way, the flexure strips 150 ordinarily exert minimal

25 influence on the measured responses to mechanical perturbations, unless they are used to "pre-load" the sensors 106 as discussed below. Useful materials for the flexure strips 150 include metallic and polymeric films. For example, one particularly useful flexure strip material is

30 polyimide film, which is available from DuPont under the trade name KAPTON in thickness ranging from about from about thirteen ,um to about one hundred twenty five !@. Other useful flexure materials include stainless steel foil, diaphrams (in general) and corrugated bronze, for example,

35 the flexure may be mechanically machined stainless steel. Since the effective spring constants of the diaphragms 166 and typical sensors 106 are temperature-dependent, the use of thermally insulating sheathing 160, 162, 164 on the shafts 120 permits the PDMA 100 to vary the temperature of the

40 sample arrays without significantly affecting the measured response.

of air bearings often make them impractical for use with a PDMA employing relatively large numbers of probes 104. 45

As noted previously, an important feature of the PDMA 100 is its ability to screen materials based on many different physical properties. One way the PDMA 100 achieves this flexibility is by using interchangeable (and, in some embodiments, disposable) test fixtures 118 with an appro-priate sample array format and sample holder 102. For example, one screening method may employ a probe 104 equipped with a ball-tip indenter test fixture 118 to rank the hardness of material samples arrayed on a rigid plate. Another screening method may employ a probe 104 fitted with a flat-tip stylus test fixture 118 to deduce Young's modulus from flexure measurements of material samples arrayed on a flexible substrate. In either case, the PDMA100 should provide a mechanism for removing and securely attaching the test fixtures 118. Suitable attachment mecha-nisms include mechanical and electromagnetic couplings, as well as devices employing permanent magnets.

FIG. 2, which illustrates the use of two flexure strips 150 to align the probes 104 with the sample array elements, shows a cross-sectional view of one of the isolation block modules 124 as seen through a cutting plane containing centerlines of the apertures 122 shown in FIG. I. The flexure 50

strips 150 are sandwiched between generally planar surfaces of upper 152 and intermediate 154 segments of the isolation block module 124 and between generally planar surfaces of the intermediate 154 and lower 156 segments of the isolation module 124. The two flexure strips 150 shown in FIG. 2 55

comprise relatively thin (from about 101

/@ to about 102

,um) rectangular membranes having spaced-apart holes that are substantially aligned with each composite shaft 120 within the apertures 122 of the isolation block modules 124.

As shown in FIG. 2, the composite shaft 120 is comprised 60

of a rigid, substantially cylindrical core 158 and a thermally insulating outer sheathing having upper 160, intermediate 162, and lower 164 sections that are threaded onto the core 158. When installed in the apertures 122, the abutting ends of the upper 160 and intermediate 162 sections of the 65

sheathing and the intermediate 162 and lower 164 sections of the sheathing lie in planes containing the two flexure

US 6,936,471 B2

9

core 158 of the shaft 120 to the second end 196 of the base 192. The test fixture 118 is removably attached to the first end 194 of the base 192 by magnetic flux originating from the permanent magnet 190 that is embedded in the base 192 of the probe 104. A tubular magnetic shield 200, which 5

typically has a lower modulus than either the probe base 192 or the permanent magnet 190, is wedged into an annular space between the probe base 192 and the permanent magnet 190. The shield 200, which helps secure the magnet 190 within the probe base 192, extends outward from the first 10

end 194 of the base 192 and mates with a substantially circular slot 202 formed in the test fixture 104. The slot 202

10

threaded holes 248 in the upper support plate 236 are substantially aligned with through-holes 250 in the first sensor board 232. The non-threaded holes 248 and the through-holes 250 are sized to provide passageways for rods 252 that transmit forces from the composite shafts 120 to sensors 106 mounted on the second (lower) sensor board 234. The PDMA 100 thus maintains the most preferred spacing by distributing the force sensors 106 among two boards 232, 234-thereby doubling the surface area avail-able to mount the force sensors 106-and by arranging the sensors 106 so their centers 126 are nine-mm apart when projected on the surface of the sample array 230. When using smaller sensors or when nine-mm spacing is not desired, the PDMA may dispense with one of the two sensor is sized to receive the tubular shield 200 with minimal

interference, and the shield 200 has a tapered end 204 that helps guide it into the slot 202 during attachment of the test fixture 118 to the probe base 192. In the embodiment shown in FIG. 3, the test fixture 118 and the probe base 192 include flanges 206, 208 for accessing them during removal or attachment.

15 boards. As many sensor boards as is practical for a particular embodiment may be employed.

FIG. 5 and FIG. 6 provide further details of the sensors 106 and sensor boards 232, 234, showing respectively, a bottom perspective view and a close-up top view of the first

20 sensor board 232. The first 232 and second 234 sensor

As can be seen in FIG. 3, the test fixture 118, the base 192, and the shield 200 enclose the permanent magnet 190, which helps minimize stray magnetic flux that may influence sample measurements of nearby probes 104. Generally, the probe 104 components are made from materials having a high magnetic permeability-a relative permeability sub- 25

stantially greater than unity-to ensure effective magnetic shielding. Suitable materials include nickel-iron alloys con-taining copper, molybdenum, or chromium and mixtures thereof. A particularly useful shielding material is available under the trade name HI-PERM 49 from Carpenter Tech- 30

nology. Other useful shielding materials include cold-rolled steel that has been chrome-plated to resist corrosion. The permanent magnet 190 should be fabricated from a material that provides sufficient force to secure the test fixture 118 to the probe base 192 during screening. Useful permanent 35

magnets 190 include samarium cobalt magnets, ceramic ferrite magnets, aluminum-nickel-cobalt magnets, and neodymium-iron-boron magnets.

boards generally comprise a flexible multi-layer dielectric sheet 270 (e.g., polyimide) and a rigid frame 272 (e.g., FR-4 epoxy glass laminate) that is bonded to the periphery of the dielectric sheet 272. Electrically conductive traces 274 are embedded on top 276 or bottom surfaces 278 of the dielec-tric sheet 270, or between layers of the flexible sheet 270, forming a double-sided flex circuit 280. Each sensor 106 is mounted on the top surface 276 of the flex circuit 280, and leads 282 on the sensors 106 are connected to conductive traces 274 that terminate at a standard card edge connector 284. Conventional ribbon cables can be used to link the card-edge connector 284 with peripheral recording and control devices (not shown) allowing communication between the sensors 106 and the peripheral devices.

As shown in FIG. 5, the first 232 and second 234 sensor boards include generally planar stiffeners 286 (e.g., FR-4 epoxy glass laminates) attached to the bottom surface 278 of the sensor boards 232, 234 directly below the sensors 106. FIG. 4 illustrates interactions of the probes 104, the

sensors 106, and a material sample array 230. FIG. 4 shows 40

a cross sectional view of the PDMA 100 of FIG. 1 taken

Each of the stiffeners 286 has about the same footprint as the sensors 106, and helps distribute loads on, and prevent bending of, the sensors 106. Note however, the stiffeners 286 from a plane that cuts through the two isolation block

modules 124 and contains centerlines of two adj acent probes 104. During screening, each test fixture 118 portion of the probes 104 interacts with one element of the sample 230 array, which is positioned at a predefined location 108 of the sample holder 102. Movement of the sample holder 102 in a direction normal 114 to the surface of the sample array 230 results in forces that are transmitted to the sensors 106 via each probe test fixture 118, probe base 192, and composite shaft 120. Each composite shaft 120, which includes a rigid core 158 and thermally insulating outer sheathing 160, 162, 164, contacts the force sensor 106 directly or indirectly as discussed below.

The relatively large footprint of each sensor 106 shown in FIG. 4 makes it impracticable to mount all of the sensors 106 on a single plane while maintaining nine-mm spacing between centers 126 of adjacent sensors 106. Of course, using sensors with smaller footprints may allow for mount-ing in a smount-ingle plane. To provide nine-mm spacmount-ing, the PDMA 100 employs sensors 106 mounted on first 232 and second 234 sensor boards, which rest on upper 236 and lower 238 rigid support plates, respectively. Both support plates 236, 238 include holes that extend from top surfaces 240, 242 of the plates 236, 238 to bottom surfaces 244, 246 of the plates 236, 238. The holes are arrayed on nine-mm centers, and are either threaded or non-threaded.

Non-do not prevent movement of the sensors 106 in a direction normal 114 to the sample array 230 since the sensors 106 are mounted on the flexible dielectric sheet 270. Although other

45 embodiments can use rigidly-mounted sensors, the PDMA 100 shown in FIG. 1 uses sensors 106 mounted on the flex circuit 280 to allow "pre-loading" of the sensors 106 as discussed below. Pre-loading may of course be performed by other methods, which those of skill in the art will appreciate

50 from a review of this specification.

The first sensor board 232 shown in FIG. 6 also includes a plurality of through-holes 250 that are located between the sensors 106. Following assembly of the PDMA 100, the through-holes 250 are substantially aligned with unthreaded

55 holes 248 in the upper support plate 236 (FIG. 4). As noted above, the unthreaded holes 248 in the upper support plate 236 provide passageways for rods 252 that transmit forces from the composite shafts 120 to sensors 106 mounted on the second (lower) sensor board 234. Thus, the centers 126

60 of the sensors 106 and the through-holes 250 of the first

sensor board 232 are arrayed on nine-mm centers. Referring to FIG. 4-6, threaded holes 288, 290 in the upper 236 and lower 238 support plates are sized to receive set-screws 292 that the PDMA 100 can use to pre-load each

US 6,936,471 B2

11

for displacements normal 114 to the plane containing the sample array 230, but are mechanically stiff for displace-ments in other directions. Moreover, the effective spring constants of the flexure strips 150 are substantially less than the spring constants of the sensors 106 so that the flexure strips 150 ordinarily exert minimal influence on the mea-sured responses of the sample array 230 to mechanical perturbations. However, since the sensors 106 are mounted on the flex circuit 280, the set-screws 292 can apply a force to the stiffeners 286 and the sensors 106 in absence of a force on the test fixture 118. A force recorded by the sensors 106 will therefore be the sum of the force acting on the test fixture 118 and the pre-load force. Since many commercial force sensors can detect only tensile or compressive loads, pre-loading permits a compressive sensor to detect small tensile loads, or a tensile sensor to record small compressive loads, e}..'Panding the capabilities of the PDMA 100. Note that the lower support plate 238 and the second sensor board 234 both include unthreaded holes 294, 296 that provide access to the set-screws 292 in the upper support plate 236. The PDMA 100 can use a wide variety of sensors 106, including miniature force sensors. Most of the sensors 106 incorporate signal conditioning electronics. Suitable force sensors include piezoresistive micromachined silicon strain gauges that form a leg of a conventional Wheatstone bridge circuit. A useful low-compliant force sensor is available from Honeywell under the trade name FSL05N2C. The Honeywell force sensor has a 500-g range (4.9 N full scale), which is suitable for most of the screening methods described in subsequent sections. As noted earlier, many force sensors can tolerate only modest variation in tempera-ture without compromising accuracy and precision. The use of a composite shaft 120 having an insulating sheathing 160, 162, 164 (FIG. 2) permits substantial temperature variation of the sample array 230 without significantly affecting the temperature and accuracy of the sensors 106.

In an alternative embodiment, force sensors are incorpo-rated into the flexure strips 150 by placing strain gages on the diaphragms 166 (FIG. 2). Strain resulting from the application of a known force-typically a deadweight load applied to the rigid shaft 120--is recorded and used to develop a calibration curve for the force sensor. The prin-cipal disadvantage of this approach is the extensive signal conditioning requirements associated with strain gage mea-surements.

12

holder 102 and material samples 230 with a first gas that is different than a second gas blanketing the sensors 106. In this way, the PDMA can vary the environment of the material samples 230 independently of the sensors 106, while maintaining the sensors 106 at conditions different than or the same as the laboratory environment.

The environmental chamber may include devices for regulating and/or monitoring the temperature of the sample array 230 elements. Useful devices include one or more

10 heating or cooling elements placed within a gas stream that

feeds the environmental chamber containing the sample array 230. Other useful devices include an array of radiant heaters positioned adjacent to the sample array 230. Alternatively, the PDMAI00 may include resistance heaters

15 or thermoelectric devices that are attached to the sample

holder 102, which heat or cool individual or groups of sample array 230 elements. The PDMA 100 may also include devices such as thermocouples, thermistors, or resis-tive thermal devices (RTD) for monitoring the temperature

20 of individual sample array 230 elements. In some

embodiments, the PDMA 100 includes a temperature controller, such as a data acquisition board, for subjecting the sample array 230 to a desired temperature-time profile. The temperature controller automatically adjusts the power

25 supplied to the heating and cooling devices in response to signals received from the temperature monitoring devices. Typically, software running on an external computer com-municates and coordinates functions of the temperature controller and the temperature monitoring devices.

30 PDMA Control and Data Acquisition

FIG. 7 shows schematically a system 300 for data acqui-sition and control of the PDMA. As noted in the discussion of FIG. 1, the PDMA 100 includes first 110 and second 112 translation actuators for displacing the sample array 230

35 (FIG. 4) in a direction normal 114 to the probes 104. The first translation actuator 110 provides relatively coarse displace-ment of the sample holder 102; it positions the eledisplace-ments of the sample array 230 near the probe 104 test fixtures 118, and can be regulated using a DC motor controller (not

40 shown). The second translation actuator 112 provides rela-tively fine displacement of the sample holder 102 and is responsible for carrying out mechanical perturbations of the sample array 230 elements.

The second translation actuator 112 shown in FIG. 7

45 comprises a piezoelectric translation stage. A primary data acquisition board 302 (e.g., National Instruments 6030E), which is located in an external computer 304, controls the operation of the second translation actuator 112. The pri-Referring again to FIG. 1 and FIG. 2, the PDMAI00 may

include an environmental chamber (not shown) that encloses the sample holder 102, the probes 104, and the upper 152 or intermediate 154 segments of the isolation block modules 124. The chamber may be filled with a gas of known 50

composition to study its influence on bulk physical proper-ties of the sample array 230 elements. Or the chamber may

mary board 302 generates a voltage, VI' which is propor-tional to the desired displacement of the actuator 112 (and sample holder 102). This voltage is fed to a piezoelectric amplifier 306 that monitors the position of the actuator 112 via a capacitive position sensor 308. In response to V l ' the

piezoelectric amplifier 306 varies the charge, V 2' which it

supplies to the actuator 112 to move the sample holder 102 to its desired position. The position sensor 308 generates a be filled with an inert gas to reduce oxidation of the sample

array 230 elements during screening. Generally, the annular gap 168 between the composite shafts 120 and the cylindri- 55

cal apertures 122 is minimized to limit the flow of gas out of the isolation block modules 124. In addition, the flexures 150 in the annular gaps 168 restrict gas efflux from the isolation block modules 124.

Alternatively, the environmental chamber may comprise a substantially gas-tight enclosure that surrounds the sample holder 102, the probes 104, the isolation block modules 124, and the sensors 106. The enclosure may be further separated into two compartments-one that encloses the sample holder 102 and the material samples 230, and one that encloses the sensors 106 and the isolation block modules 124. The latter embodiment allows blanketing the sample

voltage, V 3' which is read by the amplifier 306 and indicates

the actual position of the second translation actuator 112. As shown in FIG. 7, the primary data acquisition board

60 302 and the external computer 304, respectively, read and

record V3. In response to the value of V3, the primary board

302 updates Vias necessary and generates a timing pulse, which triggers acquisition of V 3 from the position sensor 308, thereby synchronizing signals VI and V3 . The

acqui-65 sition of V3 also generates a second timing pulse, V 4' which triggers acquisition of voltages V 5 i' V 6 i' and V 7 i' from the